Abstract

Glyphosate needs to be partnered with other herbicides that have residual biological activity on ryegrass (Lolium multiflorum Lam.) to improve the efficacy and consistency of annual ryegrass control in corn. Five field experiments were conducted from 2019 to 2021 near Exeter, Ontario to evaluate various glyphosate tank mixes applied preplant (PP) in the spring in corn for the control of annual ryegrass seeded as a cover crop in the fall of the previous year (2018 to 2020). At 1 week after application (WAA), all glyphosate tank mixes evaluated provided minimal annual ryegrass control (14-28%). At 2 WAA, the addition of dimethenamid-p/saflufenacil to glyphosate improved annual ryegrass control from 55% to 68%; there was no improvement in annual ryegrass control with the other 14 tank mixes evaluated. At 3 WAA, the addition of dimethenamid-p/saflufenacil and mesotrione + rimsulfuron to glyphosate controlled annual ryegrass 91 and 90%, respectively. At 4 WAA, the addition of dimethenamid-p, dimethenamid-p/saflufenacil, mesotrione + rimsulfuron, S-metholachlor, or bicyclopyrone/mesotrione/S-metolachlor to glyphosate improved annual ryegrass control 7, 7, 10, 8, and 6%, respectively. At 6 WAA, the addition of pyroxasulfone, pyroxasulfone + atrazine, dimethenamid-p, dimethenamid-p/saflufenacil, mesotrione + rimsulfuron, S-metholachlor, atrazine/S-metolachlor, or bicyclopyrone/mesotrione/S-metolachlor to glyphosate improved annual ryegrass control 10, 9, 12, 10, 17, 13, 10, and 12%, respectively but the addition of all other herbicides to glyphosate did not improve annual ryegrass control. Density and biomass reductions of annual ryegrass with glyphosate tank mix evaluated generally followed a similar trend as the visible control. Annual ryegrass interference reduced corn yield by up to 83% compared to the non-treated control. The addition of a residual herbicide to glyphosate did not result in an improvement in the seed yield of corn. Among the glyphosate tank mixes evaluated glyphosate + mesotrione + rimsulfuron provided the most consistent control of annual ryegrass in corn.

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